1. Field of the Invention
This invention is related to chemical composition delivery systems and methods, especially to the chemical delivery systems for electronics specialty chemical compositions, including CMP slurries for wafer polishing.
2. Related Art
Process chemicals for semiconductor manufacturing are usually delivered from bulk containers to user stations with so called chemical delivery systems. High-pressure inert gases, such as nitrogen gas, have become popular for driving chemical compositions from chemical containers to user stations. Compared to the delivery systems having a pump, systems employing high-pressure inert gas for chemical delivery have the advantages of delivery from further distance, and also smooth and pulse-less delivery, thus avoiding impurity shedding from the components of the delivery system.
Although the advantages of such a chemical delivery method have been realized and the method has been practiced in large extent, some concerns and problems have arisen when some of the semiconductor process chemical compositions are delivered with this type of delivery system. For example, inert gas, such as nitrogen gas, will readily dissolve into some of these process chemicals during compression process and eventually form dry spots on wafers. These dry spots become manufacturing defects and seriously reduce the production yield of semiconductor manufacturing. To avoid and eliminate the problem of gas dissolving in chemical compositions, a new delivery system with a bladder installed inside the pressure vessel has been invented. With this method and apparatus, high-pressure nitrogen gas is filled into the bladder to pressurize chemical compositions outside of the bladder. Since there is no direct contact between the chemical composition and nitrogen gas, dissolving of nitrogen gas into chemicals is avoided. Furthermore, chemical compositions will not change in assay due to chemical evaporation.
When delivering aqueous chemical compositions using direct contact with an inert gas, such as slurry compositions used for polishing wafer surfaces, water and other chemical compounds in the chemical composition at the composition surface and composition residuals on the container surfaces will be rapidly lost into the inert gas when the high-pressure inert gas directly contacts with the chemical composition. This is because inert gases are usually very dry and very pure. Amounts of chemical compounds such as water in the chemical composition will change because of evaporation. This change in chemical composition may make the chemical composition function improperly when it is used in the semiconductor manufacturing process. When water evaporates into inert gas, a dry film or dry residuals could be formed with much less water and more concentrated compositions of less volatility. In the case of slurry compositions, this dry film or dry residuals will be in the form of agglomerated particles of larger sizes. These agglomerated particles eventually will be delivered with chemical compositions to user stations and produce scratches on wafer surfaces. This problem could be solved by using the above mentioned bladder technology by preventing the direct contact of nitrogen gas with chemical composition. With this technology, a thin and flexible material that is compatible with the chemical composition must be carefully selected for the bladder.
To overcome the shortcomings of water evaporation into inert gas, a moisturizer can be used to moisturize the nitrogen gas prior to its going into the pressure vessels to pressurize chemical compositions, such as depicted in U.S. Pat. No. 6,076,541. When the moisturized nitrogen gas contacts with chemical compositions, mass transfer of water in the nitrogen gas and the chemical composition is significantly reduced or completely eliminated. Therefore, there is no, or very little, dry residuals or dry film formed within the pressure vessels. However, there are still some drawbacks. First, more space will be needed for accommodating a humidifier near to the pressure vessel. This could be a serious problem because in a semiconductor manufacturing facility, space is always limited. Additional equipment to occupy space is not always permitted and space is not always affordable. Second, moisturized nitrogen gas may create some problems in the system operation. Since moisturized nitrogen flows through a relative long line into the pressure vessel, moisture in nitrogen gas can be condensed in the line because of changes of physical condition. This condensate could block up valves and make the valves malfunction. The condensate could also be carried further into the pressure vessel to dilute the chemical compositions. Chemical composition change by such kind of dilution is forbidden because the composition of chemical compositions must be precisely controlled to meet user's specification. Further, some chemical compositions, such as hydrogen peroxide in the chemical composition, will evaporate into high purity inert gas even though it is moisturized. Hence, chemical compositions will change when the chemical composition is delivered with such a method although such a change in chemical composition may not be a serious problem for some cases.
It would therefore be advantageous, and an advance in the chemical delivery art, if chemical delivery systems and methods could be designed that reduce or avoid the above-noted drawbacks.